This invention relates to steel having an excellent vibration attenuation performance in addition to such basic characteristics of steel as the strength, toughness, corrosion resistant characteristic, and weldability and a method of manufacturing the same.
In recent years, vibrations and noises are restricted by laws or regulations as a source of public hazard. Moreover, vibrations generated by household electric appliances, business machines, traffic and transporting machines and various mechanical facilities cause fatigue damage of such machines and component parts thereof so that prevention of vibration is important to elongate their lives. Various attempts have been made to decrease the detrimental effects of the vibration. Among various solutions may be mentioned increase in the mass and rigidity of a member acting as a source of vibration, and an appropriate design effective to avoide dangerous resonance. Such solutions are inadvantageous in machines and apparatus whose accuracy and balance have already been investigated in a range permissible from the standpoint of economy since excess equipments must be added thereto. Elastic materials have been used for damping vibration. Such elastic materials as rubber and plastics have mechanical characteristics different from those of metallic materials. Use of such elastic materials increases the volume of the machine and cost of manufacturing. If it were possible to construct members acting as the source of vibration or vibration transmitting members with metallic materials having a high attenuation performance it would be possible to efficiently decrease undesirable vibrations without affecting basic design. Consequently, research has been made to find out metallic materials having high attenuation performance. As a consequence, Mg alloys in which a small quantity of Zn is incorporated into Mg, Mn-Cu alloys consisting essentially of Mn and Cu, and NiTi alloys containing Ni and Ti at a ratio of 50:50 have been developed. However, the Mg alloys have low mechanical strength so that they can not be used to manufacture ordinary mechanical component parts. Although Mn-Cu alloys and NiTi alloys have a relatively high mechanical strength and excellent vibration attenuation performance at or near room temperature, since their vibration attenuation performance depends upon interaction between the lattice vibration and the transformed twin crystal their operating temperature is limited to below about 80.degree. C. so that it is impossible to use these alloys to construct internal combustion engines, electric motors and component parts thereof which generate vibrations. Composite vibration absorbing member comprising two steel plates and an elastic member interposed therebetween has been widely used. However, since the elastic member has poor heat resistant property so that its operating temperature is limited to approximately 80.degree. C. On the other hand, steels relating to ferritic stainless steel containing about 10% of chromium and ferritic stainless steel containing about 10% of chromium and a large quantity of aluminum attribute their vibration attenuation performance to the interaction between the lattice vibration and the movable magnetic domain walls of steel they can maintain high attenuation performance up to a temperature near 300.degree. C. but as they are in the form of a single phase of ferrite and do not undergo any phase transformation below their melting points it is impossible to be hardened by heat treatments. For this reason, they can not be used to construct mechanical parts requiring high mechanical strength, for example, power transmission gears, lath parts, etc.